A communication system is formed, at a minimum, of a sending station and a receiving station interconnected by way of a communication channel. Data to be communicated by the sending station to the receiving station is converted into a form to permit its communication upon the communication channel to the receiving station. When received at the receiving station, the informational content of the data is recovered, or otherwise recreated, thereby to provide the receiving station with the data transmitted by the sending station.
In a radio communication system, the communication channel is formed of a radio channel, defined upon a portion of the electromagnetic spectrum. A wireline connection is not required to interconnect the sending and receiving stations of a radio communication system. Because a radio communication channel is used to effectuate the communication of data by the sending station to the receiving station, thereby obviating the need of a wireline connection therebetween, use of a radio communication system to communicate therethrough is of particular advantage when formation of the wireline connection would be inconvenient or impractical.
To convert the data to be communicated by the sending station in a radio communication system into a form to permit its communication upon a radio channel, a radio frequency (RF) carrier signal is combined together with the data to be communicated by the sending station in a modulation process. The data is sometimes referred to as being modulated upon the carrier signal. Once modulated, the resultant communication signal is of a form to permit its communication upon the radio channel formed between the sending and receiving stations.
A radio device which provides for both the sending station and a receiving station at a common unit is sometimes referred to as a radio transceiver. Two-way communication is permitted through the use of a radio transceiver.
A cellular communication system is exemplary of a multi-user radio communication system, usage of which has achieved wide popularity in recent years. A subscriber to a cellular communication system communicates therethrough by way of a radio transceiver, typically referred to as a mobile station. Mobile stations conventionally are constructed to mimic the operation of a conventional, wireline telephonic device. Because a radio link is formed between the mobile station and other portions of the cellular communication system, the need for a wireline connection to the mobile station is obviated. Communication by way of a cellular communication system is possible from locations at which formation of a wireline connection would be inconvenient or impractical.
In an ideal communication system, the communication channel formed between the sending and receiving stations does not distort the informational content of the data communicated thereon to the receiving station. However, in an actual communication system, the data is susceptible to distortion through, e.g., the introduction of Inter-Symbol Interference (ISI) fading, and interference caused by other co-generated signals and noise. Radio channels are particularly susceptible to such distortion.
Various manners have been developed by which to compensate for the distortion introduced upon the data when transmitted upon a non-ideal communication channel. Coding techniques, for instance, have been implemented, sometimes to increase the redundancy of the data so that, if portions of the data are distorted to an extent to prevent recovery thereof, the increased redundancy of the data shall still permit remaining portions of the data to be recovered, thereby to recover the informational content of the data.
Biorthogonal coding, for instance, is a manner by which to code data which is to be communicated during operation of a communication system. A biorthogonal code is a special class of lattice codes. Generally, a biorthogonal code is constructed by augmenting an orthogonal set of M/2 signals with the negatives of each signal. Biorthogonal codes are geometrically represented by the vertices of a hypercube in N dimensions. That is to say, the codes are constructed using N/2 unit vectors and their corresponding image vectors about an origin.
Conventionally, biorthogonal codes are used to perform waveform coding, a procedure by which to make each of the waveforms of a coded set of signals us unalike as possible. In other words, the goal of waveform coding is to render the cross-correlation amongst all pairs of signals as small as possible. And, the smallest possible values of cross-correlation occur when the signals are antipodal. Biorthogonal codes are optimal in terms of a distance property. Also, a codeword is implemented with a reduced number of bits relative to a conventional, orthogonal code.
A manner by which to implement biorthogonal coding in a higher-dimensional modulation scheme, such as one utilizing a N-dimensional spherical code, would advantageously improve communication quality in a communication system.
It is in light of this background information related to communication of data in a communication system that the significant improvements of the present invention have evolved.